Seven strains of Rhizobium sp. were cultured in liquid mediums using soil as the sole source for phosphorus to investigate effect of the strains on mobilization and release of phosphorus in soil. The control treatment was set in the same way except inoculation of Rhizobia . Results suggest that the bacteria released a large amount of hydrogen ions, thus making the concentration of the ions multiplied by at least 20 times, which resulted in a significant decrease in pH of the solution. Different strains of Rhizobia released different types and amounts of organic acids, including oxalic acid, malic acid, succinic acid, formic acid, acetic acid, citric acid and lactic acid. However, most of the strains exuded acetic acid. The treatments were significantly higher than the control in total phosphorus in the liquid culture mediums, while the total inorganic phosphorus in the soil immersed in the liquid behaved otherwise. Taking into account the soil being the sole phosphorus source, it could be concluded that Rhizobia could promote mobilization and release of inorganic phosphorus from the soil. Correlation analysis shows that total phosphorous was extremely positively related to pH of the liquid (r= 0.893^﹡﹡，n = 8), suggesting that the secretion of hydrogen ions from the bacteria is one of the causes for dissolution of inorganic phosphorus in soil. Inoculation of Rhizobia reduced occluded phosphorus in the soil remarkably, and also Al-P, Fe-P and Ca-P but to an extent varying with the stains of Rhizobia , which might be attributed to the different amounts and types of organic acids they could secret. The phenomenon of Rhizobia releasing hydrogen ions and a variety of organic acids suggests that inorganic phosphorus in the soil is mobilized in a number of ways, which demonstrates that inoculation of Rhizobia may help legume crops make use of various forms of unavailable phosphorus in the soil, thus making them adapted to different soils low in phosphorus.